Means and method of controlling high tension electrical circuits



March 24, 1959 T. H. ROGERS ETAL 2,879,404

MEANSTE1:IIgI METHOD OF CONTROLLING HIGH 0N ELECTRICAL CIRCUITS FiledMay 2. 1956 5 Sheets-Sheet 1 PULSE FORMING AND TIMING CIRCUIT Fl .I

I 5 4 FILM CHANGER I I 56 I U I I F|G 5 OPTIONAL 52 I f glIfr PRIMARYPOWER AND OONTROL cmcun's I 53/'I l /57 HIGH VOLTAGE POWER EQUIPMENTPULSE FORMING SUPPLY AND TIMING CIRCUIT IO 55 INVENTOR.

THOMAS H. ROGERS BY GORDON F. BAVOR ATTORNEYS March 24, 1959 T. H.ROGERS ETAL 2,879,404

MEANS AND METHOD OF CONTROLLING HIGH TENSION ELECTRICAL CIRCUITS FiledMay 2, 1956 3 Sheets-Sheet 2 FIG. 2

sxasrme x RAY IGENERATOR CONTROL I UNIT PULSE MONITOR INVENTOR.

moms H. ROGERS BY GORDON F. BAVOR ATTDRNEYS March 24, 1959 TENSIONELECTRICAL CIRCUITS 3 Sheets-Sheet 3 Filed May 2, 1956 w 6E 5&3 523 mm+m 1 +0 I W ml II W 55855 w 3 5. 3 .l

INVENTOR.

THOMAS H. ROGERS GORDON F. BAVOR United States Patent 2 'MEANS ANDMETHOD OF CONTROLLING HIGH TENSION ELECTRICAL CIRCUITS Thomas Rogers,New Canaan, and Gordon F. Bavpr, Nor-walk, Conn., assignors to 'MachlettLaboratories, Incorporated, Springdale, -Co'nn., a corporation ofConnecticut Application May 2, 1956, Serial'No. 582,252 '7 Claims.romeo-9's This invention relates to novel means and method 'ofcontrolling high=tension electrical circuits and has particularreference to-a system and methodtor controlling theop'eration of a highvoltage'eriergy-'responsive device whereby the devicemay be subje'c tedtohigh voltage for precise ultra-short periods of time. Still morespecifically this invention refers to a system and method for controlling the operation of a high voltage device suchas an X=raytube "orthe like so as toprovide precisely timed ultra-short X-ray'exposures ina selected range such as from-one to five milliseconds.

In radiography the problems concernedfwith exposure duration arecomplicated where motion is involved in the subject matter and theproblem of obtaining sharp, clearlimages becomes more and morecomplicated as the speed of motion increases. These problems are-solvedby therprovision of more precise, shorter-interval timers and moreXi-rayprod'ucingpower in a fine focus X-r'ay tube.

.X-ray apparatushas become increasingly'more capable in theserespects.First, radiography at 4 second was evolved and later 43 second exposuresbecame feasible. Fairly recently, however, it became desirable in workwith heart radiography, particularly angiocardiography, to obtain. stillshorter exposures in rapid succession, such as severalper second.

Conventional high-powered generators havesometimes been used for thispurpose and in these instances the basic circuit of the generatorinvolved the opening and closing of a switch in the primary circuit of ahigh-tension transformer. This required carefulconsideration, in thedevelopment of timing and contacting systems, of the proper phasing ofthe instancofcontact make and break witht'he sine-wave of the powersupply. Such considerations generally limited possible timeintervals tointegral multiples of a one-cycle period of the AC. power supply.Recently developedsystemsperrnit using an odd number of half-cycles,with minimum durations of second.

Other known prior art indicates that efforts have been tension orsecondarysideofthe circuit. This invention comprises improved andnovel-means and method of-accomplishing the control=ofsuch exposures byswitchingin the high-tension circuit.

It is a primaryobject of this invention to provide a system forcontrolling the operation of high voltage energy responsive devices suchas X-ray tubes or the like whereby the devices may be'subjected to highvoltage for precise ultra-short periods of time.

It is another object of this invention to provide a system forcontrolling the operation of an X-ray tube so as to provide preciselytimed ultra-short exposures in a selected range such as'from one to fivemilliseconds.

Another object is to provide a system of the above characterwhichisadapted to existing diagnostic or other equipment.

-A further object is theprovisiori ofva simplified system of, the abovecharacter which requires low control-circuit l atented N lar. Zfl,

voltage and power requirements as well as relatively simple controlcircuitry.

A still further object is the provision of a system of the abovecharacter which embodies novel safety means for preventing damage to thehigh voltage device in the event of control voltage 'failure in the highvoltage circuit.

Other objects and advantages of the invention will become apparent fromthe following descriptiontakenin connection with the accompanyingdrawings, in which Fig. 1 is a simplified schematic diagram of thecircuit of the switching system;

Fig. 2 shows the circuit details involved in supplying the variouspotentials required for the operation of the switching tube, andalsoshows the safety circuit, thegrid return circuit, and the method ofcutting the electronic switching system in or out;

Fig. 3 is a block diagram showing the various component parts of thesystem of the present invention as used with existing film changingequipment; and

Fig. 4 shows the'basic circuit of a pulse generator usable with thissystem.

In the drawings the system is shown as being used for controlling theoperation of an X-ray tube but it is to be understood that other highvoltage energy responsive devices can be substituted for the X-ray tubeif desired.

The circuit of the presently described system is employed in conjunctionwith a rectified X-ray generator having electrical energy storage meanssuch as capacitors across the output whereby the generator, which isenergized 'inadvance of making the exposure, chargesth'e capacitors toits full open-circuit voltage, and the exposure is then made at thatvoltage. The power'for energizing the X-ray tube comes directly from thecapacitors and, therefore, the need for synchronizing the exposure withthe sine-wave power operating the transformer is eliminated. Also, insuch a system, essentially square pulses are drawn fromthe capacitors.

A pulse forming and timing circuit generates a control signal in theform of an essentially square voltage pulse, the width of which can beadjusted over a suitable range. The signal is applied to the controlgrid of a switching tube through a pulse transformer which transmitssquare pulses five milliseconds or less in width without appreciabledistortion. The pulse transformer also isolates the control circuit fromthe high-tension part of the system.

The control grid bias, screen grid potentials, and filament power forthe switching tube are provided by an isolation transformer throughsuitable rectifiers and filters.

Embodied inih'e system also is asafety circuit which is provided toprotect thee'quipment from damage in the event of loss of negative biason the switch tube ineasecircuit which minimizes driving powerrequirements by.

bypassing thecurrent drawn by the controlgrid, during exposure.v periods"of the X-ray tube, around the bias su 1 ply without'the use of ashunting resistor.

- single oil-'filled tank for insulation reasons.

Withinthe tankis' also located an auiriliarymulti'polef high-tensionswitch, solenoid-operated by -re'rnote con and the X-ray tube bysheckproo'r r 1 3 trol, by which the electronic switching system,including the energy storage capacitors, can be cut in or out of thecicuit at will. Thus, the X-ray equipment can be used conventionally ifdesired.

Referring to the drawings, and more particularly to the schematicdiagram of Fig. 1, it will be seen that a pulse-forming and timingcircuit 10 is provided for generating a control signal in the form ofanessentially square voltage pulse P which is applied to the controlgrid of a switching tube 11 through a pulse transformer 12. Thepulse-forming and timing circuit 10, to be described later, allowsadjustment of the pulse within a suitable range. The pulse transformer12 transmits square pulses of controlled width such as aboutmilliseconds or less without appreciable distortion and also serves toisolate the control circuit from the high tension part of the system.The primary of pulse transformer 12 is connected directly into thecircuit 10. A negative bias for the control grid of the switching tube11 is provided by a suitable D.C. power supply 13. This negative bias isapplied to the control grid of the switching tube through the secondaryof pulse transformer 12. Special circuitry is provided to apply thisnegative cut-off bias to the control grid of the switching tube 11, aswill be described more fully hereinafter with respect to Fig. 2.Positive screen grid potential in tube 11 is provided by a second D.C.power supply 14.

A high voltage generator 15 such as a four-valve fullwave bridgerectifier type as illustrated in Fig. l is utilized to charge two energystorage capacitors 16 in a balanced circuit as the primary source ofenergy for the X-ray tube 17. The high voltage switching tube 11 is inseries with the positive side of the high voltage generator circuit tothe anode of the X-ray tube 17.

- The generator 15 is energized in advance of making an exposure withthe X-ray tube 17 and charges the condensers 16 to its full open-circuitvoltage, and then the exposure can be made at that voltage. In theabsence of the capacitors 16, the power for energizing the X-ray tube 17would come directly from generator 15, in which case the exposurevoltage would be considerably below the open-circuit voltage of thegenerator 15 due to the regulation of the transformer therein, and thepower line. The switching tube 11 and the insulation of the system also,in the absence of the capacitors 16, must withstand the fullopen-circuit voltage. Since the power for energizing the X ray tube 17comes from the capacitors 16, in accordance with this invention, insteadof directly from the generator 15, the need to synchronize the exposurewith the sine-wave of the power'line is eliminated. With the presentsystem the only time'it may be desirable to synchronize the exposurewith the power line frequencies might be in the event that it is desiredto obtain a high rate of repetitive exposures. X-ray exposure currentwave shape, pulse P1, is essentially identical to the shape of thevoltage pulse P applied to the high voltage switching tube, theamplitude of the current being limited by the emission-limitedcharacteristics of the X- ray tube 17. Y

In Fig. 2, all switches, relays, and the like are shown in the positionsthey occupy when the system of the present invention is installed in,but is not electrically switched into, the existing X-ray equipment andno power is applied to the system, line switch 41 being open.

The control grid bias and screen grid potentials of switching tube 11are provided by an isolation-transformer 18'with multiple secondaries,throughsuitable rectifiers 19-20 and filters. Transformer 18 alsosupplies filament power to all tubes in the high tension system exceptX-ray tube 17. The screen potential of switching tube 11 is supplied byrectifier 20 in a full-wave center-tap type of power supply embodying asimple filter capacitor 21 and bleeder resistor 22. The control grid.negative bias supply consists of rectifier 19 in a second full-wavecenter tap type. ofpower supply comprising-a.

filter capacitor 23, bleeder resistors 24 and 25, and a bias controltube 26. This bias control tube 26 is a tetrode which is operated atcut-off in its static condition and receives its grid bias and screenpotentials from the voltage divider-bleeder resistors 24 and 25 whichform part of the negative bias supply. A coupling capacitor 27 andcontrol grid signal amplitude control potentiometer 28 are provided fordriving tube 26 from the pulse transformer 12. The purpose of tube 26 isto provide a low impedance path for the control grid pulse current ofthe high voltage switching tube 11 and a high impedance path to thenegative bias supply during the inter-pulse period, thereby reducing theaverage continuous current from the negative bias supply.

Control tube 26 minimizes driving power requirements by bypassing thecurrent drawn by the control grid of the switching tube 11 around thebias supply during exposure periods.

Also shown in Fig. 2 is the safety circuit which is provided to protectthe equipment from damage in the event of loss of negative bias on theswitch tube 11 in case of power unit failure. This circuit consists of avoltage sensitive relay 29 and a current limiting resistance 30 acrossthe negative bias supply, which relay 29 is actuated only when biasvoltage is up to normal. Relay 29 closes the circuit to a signal light31 which actuates a photocell 32 in an interlocked circuit, the chassis(not shown) which supports the photocell and associated circuitry beingat ground potential.

The photocell circuit itself is basically of conventional design butpossesses novelty in the present system by embodying a tranparent glassor plastic rod or transilluminator R which is positioned between thephotocell 22 and the signal light 31. Thus, the signal light 31, whichis part of the bias power supply, transmits light rays through thetransilluminator R to operate the photocell 22. The transilluminatorthus serves to electrically isolate the high tension circuitry fromground.

It will be understood that should the negative bias to switching tube 11fail for reasons such as, for example, short circuiting of the filtercapacitor 23, burning out of the filament in rectifier 19, power failurein transformer- 18, or for any other reason, this will cause relay 29 toopen, thus turning off signal light 31 and stopping operation ofphotocell 32, thereby recovering negative bias on a thyratron tube 33also in the circuit. Thyratron tube 33 operates on AC. and, duringoperation of the system, is in a self-rectifying half-wave condition.Thus, the negative bias on the grid of thyratron tube 33, with fallingplate voltage from the applied sine wave plate potential, allows thistube to turn itself off. This drops out plate relay 34, the contacts ofwhich are in series with the coil of interlock relay 35. Suchdeenergizing of relay 35 opens its contacts which are in series with thecoil of a primary contactor 36, which is part of the existing diagnosticequipment with which the present system is used, which contactor 36controls power to the high tension generator 15. This removes the highvoltage which charges the pulse energy storage condensers or 34 opens.

In the absence of a safety device of this character, loss of negativebias and subsequent loss of control of the high voltage switching tube11 would result in a continuing .runaway condition, even after theinitial discharge of-the energy storage condensers 16, which might causeextensive damage to the system and particularly to the X-ray tube 17.

.Arelay 38 is provided to bypass the series safety cir-' .cuitsembodying relay 35 when, in a completed installation, the presentlydescribed system is turned oif' and not being" used, so that theexisting diagnostic unit into which the present system is connected maybe operated in the normal manner.

This system includes high tension switching means for completelydisconnecting the high voltage elements o f the switching tube circuitryso that conventional radrography techniques may be performedconveniently without requiring manual changes to be made after thesystem is installed in existing equipment. The high'ten- S1011 switchingmeans consists of three ganged switches 39, 39a and 39b whichxareconnected to an actuating mechanism which comprises two solenoids 40 and40a. The switches 39, 39a and 39b in'Fig. 2 are shown in positionspermitting conventional use of the X-ray equipment, switch 39 connectingthe anode ofthe X-ray .tube 17 directly to the positive side of the hightension generator 15. It will be noted that at all times the cathode ofthe X-ray tube 17 is permanently connected to the negative side of thehigh tension-generator 15. v

"To make radiographs with this system, 'it is merely necessaryto closethe line switch 41 which will cause energization of solenoid 40.Solenoid 40 thus will actuate switches 39, 39a and 39b, and therebyconnect the present system into the existing X-ray equipment. Switch 39,inthis position, connects the anode of the X-ray tube 17 to the cathodeof the high'voltage switching tube 11. Switches 39a and 39b now connectthe high voltage sides of condensers 16 to the positive and negativesides respectively of the high voltage generator 15.

After suificient time has elapsed to permit the various tubes in thesystem to reach operating temperatures, radiographic exposures may bemade in a manner to be described hereinafter in connection with Fig. 3.

After all desired exposures have been made with the present system, thesystem may be turned off with line switch 41, which removes power fromthe system and, throughsolenoid 40a and time delay 42 which bypasses"switch 41, the high tension switches 39, 39a and 39b are returned totheir initial positions as shownin Fig. '2. The time delay 42 functionsto remove power'from the solenoid 40a after a predetermined timeinterval. High tensionswitches 39a and 39b now connect the highvoltage'side'of the condensers 16 to discharging current limitingresistors 43 and 43a respectively.

A micro-switch '44 is mechanically actuated by the high voltageswitching means and serves asa high vo1tage switch position safetyinterlock so that relay 35, which controlshigh tension generator primarycontactor 36, will not close unless the high voltage switches have beencompletely closed to-eleetrically insert this system in the existingequipment.

Signal lights are provided to indicate the proper or improper operationof or failure of power to thevarious circuits involved. Light 45indicates that power is being supplied to the pulse-forming and timingcircuit 10. Light 46 shows that power is being applied to powertransformer 18 and the safety circuit described hereinbefore. Signallight 47 operates from microswitch 44 andindicates that the hightension. switches 39, 39a and 39b are in proper position for operationof this system,

while light 48 indicates, when lighted, that theseswitches arenotproperly positioned for this purpose.

A pulse monitor circuit 50 isincorporated in the pulse-- forming andtiming circuit '10 to indicate an exposure by the X-ray tube and tofacilitate adjustment and calibrationof the X-ray tube filament circuitby indicating the peak X-ray tube current in the presently describedpulsed operation. The unit making up the pulse monitor 50 is essentiallya peak voltmeter which reads the voltage drop .across a currentviewing'resistor 49 in the center tap ground circuit of the energystorage capacitors 16.

Referring to Fig. 3, it .is to be understood that the system of'thepresent invention is adaptable for use with various types ofconventional film changing devices. The present system may be used tocontrol the film changer or may be partially controlled by the filmchanger. For example, a film changer is .indicatedby numeral 51 in Fig.3and is shown connected to the pulse'forming and timing circuit 10through a manually operable selector switch 52 which allows selectivemanual or automatic control of'the system. Switch '52 is shown inposition to permit manual operation of the system whereby X-rayexposures may be made without using the film changer 51, the systembeing operated'by manual closure of push button 53 to permitexposures tobe'made. When switch 52 is moved'to the opposite position, this connectsthe film changer 51 into the system in such a manner that the filmchanger actually controls X-ray exposures to the extent that noexposures can be made, even when pushbutton 53 is operated, until thefilm changer 51 has completed its automatic cycle. It is particularlypointed out that an operator has constant control of the device duringthe actual exposure cycles by being required to actuate push button 53before any-exposurescan be made either manually or automatically.

An optional recycling circuit 54 can be provided for use with certainfilm changers where it is needed or desired such as, for example, ininstances where the film changer will not function without a recyclingsignal or is not of the free running type. Such a recyclingcircuit 54thus can be used to start operation of the film changer 51 aftercompletion of an X-ray exposure.

'Fig. 3 also shows that the pulse forming .and timing circut 10 receivespower, whenline switch 41 is closed, through the power supply 55. The'primary power and control circuits 56 also receive power when switch 41is closed and control'the power to the high voltage equipment 57, asdescribed in detail in connection with Fig. 2.

An example of one fundamental pulse forming and timing circuit capableof being used in this system is shown in Fig. 4. This circuit,indicated'by numeral 10 in Figs. 1, 2 and 3, embodies a pulse generatorfor forming the substantially square pulses which are transmitted to thepulse transformer 12, and is adapted to form pulses of controlled widthand voltage. A pulse amplifier is alsoincluded to increase the powerlevelof the pulses developed by the generator, and a synchronizingtrigger circuit is also embodied for initiating'the formation of pulsesby the generator when the push butto 53'is manually operated.

The pulse generator may be of any suitable design and is shown in Fig. 4as a driven monostable cathodecoupled multivibrator which is comprised,in this particular structure, of two triodes 58 and 59. Thismultivibrator is driven by a synchronizing amplifier tube 60 whichis'connected in parallel with tube 58.

The pulse width is manually adjustable over the desired range by meansof a potentiometer 63 which varies the time constant of the timingcontrol circuit'of the multivibrator, which -circuit includes-acapacitor 64 as well as the potentiometer 63.

The pulses developed by the pulse generator are amplified by a vacuumtube amplifier 61 to a predetermined power level controlled by meanssuch as a grid driving controlpotentiometer 62. The plate circuit of thepulse amplifier 61 is connected to the primary of the pulse transformer12.

'It is apparent from the foregoing description thata be understood,however, that although the individual.

' parts of the system have been shown and described specifically, manyof these parts may be modified within the scope of this inventionsuchas, for example, bysubstituting a thyra'tron or other pulse formingcircuit for the pulse forming and timing circuit 10, or by use of -7.other types of rectified high voltage generators other than generator15.

It is also to be understood that although a major portion of thepreceding description relates to a system for controlling an X-ray tubeso as to provide precisely timed ultra-short X-ray exposures, the systemcan be used for other purposes such as, for example, to apply pulsesshorter than or longer than one millisecond to energy responsive devicesof the type used in radar transmitters, particularly klystrons designedfor operation at relatively high voltage levels. In some instances,also, the energy storage capacitors may be eliminated whereupon thepower for energizing the energy responsive device will be provideddirectly from the generator.

Accordingly, while the novel features of the invention have been shownand described and are pointed out in the annexed claims, it is to beunderstood that various omissions, substitutions and changes in thedetails shown and described may be made by those skilled in the artwithout departing from the spirit of the invention. Therefore, it is tobe understoodthat all matter shown or described is to be interpreted asillustrative and not in a limitingsense.

We claim:

1. A system for operating a high tension circuit embodying an energyresponsive device by means of a low tension control circuit, comprisinga generator in the high tension circuit, electrical energy storage meansacross the output of the generator and adapted to be charged to the fullopen-circuit voltage of the generator, one side of the energy storagemeans being connected to the energy responsive device, a high voltageswitching tube of the tetrode type connected between the other side ofthe storage means and the energy responsive device, means connected withthe switching tube for providing control grid bias and screen gridpotentials thereon, pulse forming and timing means in the low tensioncircuit for generating a control signal in the form of an essentiallysquare voltage pulse, and a pulse transformer between the high and lowtension circuits adapted to receive the pulse from the pulse forming andtiming means and to apply the pulse to the grid of the switching tube tocause discharge of energy from the energy storage means to the energyresponsive device.

2. A system for operating a high tension circuit embodying an energyresponsive device by means of a of the generator, one side of the energystoragemeansbeing connected to the energy responsive device, a highvoltage tetrode switching tube connected between the other side of thestorage means and the energy responsive device, means connected with theswitching tube for providing control grid bias and screen gridpotentials thereon, a pulse forming and timing means in the low tensioncircuit for generating a control signal, a pulse transformer between thehigh and low tension circuits adaptedv to receive the control signalfrom the pulse forming and timing means and to apply the signal to thegrid of the switching tube to cause discharge of energy from the energystorage means to the energy responsive device, and a safety circuitconnected to the means for providing control grid bias to. the switchingtube comprising means for automatically discontinuing operation of thehigh voltage generator. 7

3. A system for operating a high tension circuit embodying an energyresponsive device by means of a low tension control circuit, comprisinga high voltage generator in the high tension circuit, electrical energystorage means across the output of the generator and'adapted to.

be charged to the full open-circuit voltage of the generator, one sideofthe energy storage means being connected to the energy responsivedevice, a high voltage tetrode switching tube connected between theotherside of the storage means and the energy responsive device, meansconnected with the switching tube for'providing control grid bias andscreen grid potentials thereonya pulse forming and timing means in thelow tension circuit for generating a control signal, a pulse transformerbetween the high and low tension circuits adapted to receive the controlsignal from the pulse forming and timing means and to apply the signalto the grid of the switching tube to cause discharge of energy fromtheenergy storage means to the energy responsive device, and asafetycircuit connected to the means for providing'control grid bias totheswitching tube comprising a voltage-1 sensitive relay across the meansfor providing control grid bias and adapted to be closed when said meansis functioning, a lamp connected with the relay so as to, function whenthe relay is closed, a photocell in the low tension circuit,transilluminating means between the lamp and photocell for directinglight from the lamp to the photocell, and means operable when thephotocell is inoperable to break the circuit to the generator.

4. A system for operating a high tension circuit embodying an X-ray tubeby means of a low tension control 4 circuit, comprising a generator inthe high tension circuit,

- voltage tetrode switching tube connected between the other side of thestorage means and the X-ray tube, pulse forming and timing means in thelow tension circuit for generating a control signal in the form of anessentially squarevoltage pulse, and a pulse transformer between thehigh and low tension circuits adapted to receive the pulse from thepulse forming and timing means and toapply the pulse to the grid of theswitching tube to cause, discharge of energy from the energy storagemeans to the X-ray tube.

5. A system for operating a high tension circuit em-' bodying an X-raytube by means of a low tension con-- trol circuit, comprising agenerator in the high tension circuit, electrical energy storage meansacross the output. of the generator and adapted to be charged to. thefull} open-circuit voltage of the generator, one side of the potentialsthereon, a pulse forming and timing means in energy storage means beingconnected to the X-ray tube, j a'high voltage switching tube of thetetrode type con-, nected between the other side of the storage meansand the X-ray tube, means connected with the switching tube, forproviding control grid bias and screen grid potentials thereon, pulseforming and timing means in the lowtension circuit for generating acontrol signal in the form of an essentially square voltage pulse, and apulse transformer between the high and low tension circuits adapted, toreceive the pulse from the pulse forming and timing, means and to applythe pulse to the grid of the switching tube to cause discharge of energyfrom the energy stor-, age means to the X-ray tube.

6. A system for operating a high tension circuit cmi bodying an X-raytube by means of a low tension con-.

trol circuit, comprising a high voltage generator in the. high tensioncircuit, electrical energy storage means. across the output of thegenerator and adapted to be charged to the full open-circuit voltage ofthe genera-. tor, one side of the energy storage means being con nectedto the X-ray tube, a high voltage tetrode switching tube connectedbetween the other side of the storage means and X-ray tube, meansconnected with the switching tube for providing control grid bias andscreen grid' forming and timing means and to apply the signal. tothegrid of the switching tube to cause discharge of energy 9 from theenergy storage means to the X-ray tube, and a safety circuit connectedto the means for providing control grid bias to the switching tubecomprising means for automatically discontinuing operation of the highvoltage generator.

7. A system for operating a high tension circuit embodying an X-ray tubeby means of a low tension control circuit, comprising a high voltagegenerator in the high tension circuit, electrical energy storage meansacross the output of the generator and adapted to be charged to the fullopen-circuit voltage of the generator, one side of the energy storagemeans being connected to the X-ray tube, a high voltage tetrodeswitching tube connected between the other side of the storage means andthe X-ray tube, means connected with the switching tube for providingcontrol grid bias and screen grid potentials thereon, a pulse formingand timing means in the low tension circuit for generating a controlsignal, a pulse transformer between the high and low tension circuitsadapted to receive the control signal from the pulse forming and timingmeans and to apply the signal to the grid of the switching tube to causedischarge of energy from the energy storage means to the X-ray tube, anda safety circuit connected to the means for providing control grid biasto the switching tube comprising a voltage-sensitive relay across themeans for providing control grid bias and adapted to be closed when saidmeans is functioning, a lamp connected with the relay so as to functionwhen the relay is closed, a photocell in the low tension circuit,transilluminating means between the lamp and photocell for directinglight from the lamp to the photocell, and means operable when thephotocell is inoperable to break the circuit to the generator.

Morrison Dec. 7, 1937 Quittner July 5, 1949

